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Gallium sulfide (GaS) stands out as a versatile nonlinear optical material for green–blue optoelectronic and photocatalytic nano-devices. In addition, the in-plane breaking strain and mechanical strength of layered GaS make it a promising candidate for next-generation flexible nanodevices. The fast and reliable assessment of the number of layers, without sample loss, is key for these applications. Here we unveil the influence of dimensionality in the structural, mechanical, and vibrational properties of GaS by applying density-functional theory-based quantum-simulations and group-theory analysis. We find its intralayer structure and interlayer distances are essentially independent of the number of layers, in agreement with the van der Waals forces as dominant interlayer interactions. The translational symmetry breaking along the stacking direction results in different structural symmetries for monolayers, N-odd layers, N-even layers, and bulk geometries. Its force constants against rigid-layer shear, KLSM = 1.35 × 1019 N m−3, and breathing, KLBM = 5.00 × 1019 N m−3, displacements remain the same from bulk to bilayer structures. The related stiffness coefficients in bulk are C44 = 10.2 GPa and C33 = 37.7 GPa, respectively. This insight into GaS interlayer interactions and elastic coefficients reveals it as a promising lubricant for nano-mechanic applications and it is easy to cleave for thickness engineering, even in comparison with layered graphite, MoS2 and other transition metal dichalcogenides and group-IIIA metal monochalcogenides. We present the GaS Raman and infrared spectra dependence on the layer number as strategies for sample thickness characterization and derive formulas for distinguishing the number of layers in both high and low-frequency regimes. In addition, our analysis of their optical-activity selection rules and polarization dependencies is applicable to isostructural group-IIIA metal monochalcogenides with 2H-layer stacking, such as gallium/indium sulphide/selenide. These results contribute to rapid and non-destructive characterization of the material's structure, which is of paramount importance for the manufacturing of devices and the utilization of its diverse properties. [ABSTRACT FROM AUTHOR]

This manuscript presents the Raman characterization of the stable carbon materials found in a special type of soil, named Terra Preta de Índio (Indian Dark Earths). The Terras Pretas de Índios have been studied as a potential model for sustainable agriculture in the humid tropics. The stability of organic matter and the long-term high-level of ion exchange capacity in these soils are due to unusually high amount of black carbon. Here, we show how Raman spectroscopy can be used to characterize the stable carbon content in the Terras Pretas de Índios (TPI-carbons). The tangential stretching mode (G band) and the disorder-induced mode (D band) are analyzed in comparison to laboratory-produced amorphous carbons at different degree of disorder used here as reference materials. Statistical analysis show predominance of sp2 phase and crystallite sizes within the limit range between nanographite and amorphous carbons, while Raman mapping of a TPI-carbon grain shows that the surface is more disordered than the grain core. The analysis used here can also differentiate the TPI-carbon structures from different types of charcoal. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The 'close proximity' configuration was used for field emission analysis of graphene-incorporated aluminum (Al) composites. The turn-on field was found to be 2 V μm -1 for the AlGr1 (1% graphene (by weight) inside the Al matrix) composite compared to 4.75 V μm -1 for the pristine aluminum sample. As the potential was increased, the current due to emission expeditiously increased in an electric field of 4 V μm -1 , with 1 mA cm -2 current density due to emission for the AlGr1 composite, compared to that of 1.08 μA cm -2 for Al. The turn-on value was visually perceived to be superior for the AlGr1 composite as compared to the value for Al. Also, a quite stable emission current was recorded for the AlGr1 composite as compared to Al. Furthermore, the composites maintained approximately 98.7% of the density of pure aluminum following the sintering process. The structural wholeness and the nonexistent porous quality of the sintered specimens was confirmed via X-ray micro-computed tomography (micro-CT). The thermal amalgamation of the AlGr composite materials at 640 °C was found to be adequate, and produced composites with the desired strength. These evaluations indicate that AlGr composites can be excellently applied as cathodes and for the prevention of crumpling of electrical line cables., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Au nanoparticles (NPs) are decorated on hydrothermally synthesized Bi 2 S 3 nanorods (NRs) to enhance the field electron emission (FEE) performance as compared to bare Bi 2 S 3 nanorods, resulting in reduction in turn-on field from 3.7 to 2.7 V μm -1 (at the current density of 1.0 μA cm -2 ) with significant increment in maximum emission current density from 138 to 604.8 μA cm -2 (at a field of 7.8 V μm -1 ) respectively. FESEM/TEM reveals that Bi 2 S 3 nanoflowers are assembled from Bi 2 S 3 NRs of a typical diameter of 120 ± 10 nm, and Au NPs of diameter about 5-10 nm are uniformly decorated onto the surface of NRs to form an Au/Bi 2 S 3 composite. XRD analysis suggests that the as-synthesized product consists of orthorhombic Bi 2 S 3 NRs decorated with face-centered cubic Au NPs. The XPS spectrum shows the elemental mapping of the as-synthesized Au/Bi 2 S 3 . Improvement in field emission properties is mainly attributed to a reduction in work function and increasing emitting sites due to Au NP decoration., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

The layered transition-metal dichalcogenide material 1T-TaS 2 possesses successive phase transitions upon cooling, resulting in strong electron-electron correlation effects and the formation of charge density waves (CDWs). Recently, a dimerized double-layer stacking configuration was shown to form a Peierls-like instability in the electronic structure. To date, no direct evidence for this double-layer stacking configuration using optical techniques has been reported, in particular through Raman spectroscopy. Here, we employ a multiple excitation and polarized Raman spectroscopy to resolve the behavior of phonons and electron-phonon interactions in the commensurate CDW lattice phase of dimerized 1T-TaS 2 . We observe a distinct behavior from what is predicted for a single layer and probe a richer number of phonon modes that are compatible with the formation of double-layer units (layer dimerization). The multiple-excitation results show a selective coupling of each Raman-active phonon with specific electronic transitions hidden in the optical spectra of 1T-TaS 2 , suggesting that selectivity in the electron-phonon coupling must also play a role in the CDW order of 1T-TaS 2 .

The layered mineral tilkerodeite (Pd 2 HgSe 3 ), the palladium analogue of jacutingaite (Pt 2 HgSe 3 ), is a promising quantum spin hall insulator for low-power nanospintronics. In this context, a fast and reliable assessment of its structure is key for exploring fundamental properties and architecture of new Pd 2 HgSe 3 -based devices. Here, we investigate the first-order Raman spectrum in high-quality, single-crystal bulk tilkerodeite, and analyze the wavenumber relation to its isostructural jacutingaite analogue. By using polarized Raman spectroscopy, symmetry analysis, and first-principles calculations, we assigned all the Raman-active phonons in tilkerodeite, unveiling their wavenumbers, atomic displacement patterns, and symmetries. Our calculations used several exchange-correlation functionals within the density functional perturbation theory framework, reproducing both structure and Raman-active phonon wavenumbers in excellent agreement with experiments. Also, it was found that the influence of the spin-orbit coupling can be neglected in the study of these properties. Finally, we compared the wavenumber and atomic displacement patterns of corresponding Raman-active modes in tilkerodeite and jacutingaite, and found that the effect of the Pd and Pt masses can be neglected on reasoning their wavenumber differences. From this analysis, tilkerodeite is found to be mechanically weaker than jacutingaite against the atomic displacement patterns of these modes. Our findings advance the understanding of the structural properties of a recently discovered layered topological insulator, fundamental to further exploring its electronic, optical, thermal, and mechanical properties, and for device fabrication.

Phonons play a fundamental role in the electronic and thermal transport of 2D materials which is crucial for device applications. In this work, we investigate the temperature-dependence of A[Formula: see text] and A[Formula: see text] Raman modes of suspended and supported mechanically exfoliated few-layer gallium sulfide (GaS), accessing their relevant thermodynamic Grüneisen parameters and anharmonicity. The Raman frequencies of these two phonons soften with increasing temperature with different [Formula: see text] temperature coefficients. The first-order temperature coefficients θ of A[Formula: see text] mode is ∼ -0.016 cm -1 /K, independent of the number of layers and the support. In contrast, the θ of A[Formula: see text] mode is smaller for two-layer GaS and constant for thicker samples (∼ -0.006 2 cm -1 K -1 ). Furthermore, for two-layer GaS, the θ value is ∼ -0.004 4 cm -1 K -1 for the supported sample, while it is even smaller for the suspended one (∼ -0.002 9 cm -1 K -1 ). The higher θ value for supported and thicker samples was attributed to the increase in phonon anharmonicity induced by the substrate surface roughness and Umklapp phonon scattering. Our results shed new light on the influence of the substrate and number of layers on the thermal properties of few-layer GaS, which are fundamental for developing atomically-thin GaS electronic devices.

The knowledge of the phonon coherence length is of great importance for two-dimensional-based materials since phonons can limit the lifetime of charge carriers and heat dissipation. Here we use tip-enhanced Raman spectroscopy (TERS) to measure the spatial correlation length L c of the A 1g 1 and A 1g 2 phonons of monolayer and few-layer gallium sulfide (GaS). The differences in L c values are responsible for different enhancements of the A 1g modes, with A 1g 1 always enhancing more than the A 1g 2 , independently of the number of GaS layers. For five layers, the results show an L c of 64 and 47 nm for A 1g 1 and A 1g 2 , respectively, and the coherence lengths decrease when decreasing the number of layers, indicating that scattering with the surface roughness plays an important role.

According to their sugar recognition specificity, plant lectins are proposed as bioactive proteins with potential in cancer treatment and diagnosis. Helja is a mannose-specific jacalin-like lectin from sunflower which was shown to inhibit the growth of certain fungi. Here, we report its recombinant expression in a prokaryotic system and its activity in neurobalstoma cells. Helja coding sequence was fused to the pET-32 EK/LIC, the enterokinase/Ligation-independent cloning vector and a 35 kDa protein was obtained in Escherichia coli representing Helja coupled to thioredoxin (Trx). The identity of this protein was verified using anti-Helja antibodies. This chimera, named Trx-rHelja, was enriched in the soluble bacterial extracts and was purified using Ni +2 -Sepharose and d-mannose-agarose chromatography. Trx-rHelja and the enterokinase-released recombinant Helja (rHelja) both displayed toxicity on human SH-SY5Y neuroblastomas. rHelja decreased the viability of these tumor cells by 75% according to the tetrazolium reduction assay, and microscopic analyses revealed that the cell morphology was disturbed. Thus, the stellate cells of the monolayer became spheroids and were isolated. Our results indicate that rHelja is a promising tool for the development of diagnostic or therapeutic methods for neuroblastoma cells, the most common solid tumors in childhood., Competing Interests: The authors declare no conflict of interest.

Gold is a noble metal that, in comparison with silver and copper, has the advantage of corrosion resistance. Despite its high conductivity, chemical stability and biocompatibility, gold exhibits high plasticity, which limits its applications in some nanodevices. Here, we report an experimental and theoretical study on how to attain enhanced mechanical stability of gold nanotips. The gold tips were fabricated by chemical etching and further encapsulated with carbon nanocones via nanomanipulation. Atomic force microscopy experiments were carried out to test their mechanical stability. Molecular dynamics simulations show that the encapsulated nanocone changes the strain release mechanisms at the nanoscale by blocking gold atomic sliding, redistributing the strain along the whole nanostructure. The carbon nanocones are conducting and can induce magnetism, thus opening new avenues on the exploitation of transport, mechanical and magnetic properties of gold covered by sp(2) carbon at the nanoscale.